Tire components are typically formed as elastomeric strips of a defined width that are cut to a length and wound cylindrically onto a tire building drum wherein the cut ends are abuttingly joined or overlapped to create a spliced joint.
The various components of a tire are layered onto the building drum and rigid annular bead cores are applied over the lateral ends of the cylindrical carcass and these ends are thereafter folded over the bead cores and the resultant carcass is then toroidally shaped prior to having the belt reinforcing layers and the tread applied.
To achieve the desired tire uniformity these splice joints are often cut obliquely to the transverse direction of the strip so the splice joint does not create a noticeable harmonic vibration caused by either an overlap or mass change of material at the splice. Ideally the cut ends would be joined with little or no mass variation. One way to attempt to achieve this is to cut the strips on a low skive angle, this creates an elongated chamfer surface that when overlapped creates less mass fluctuations at the cut joint. Such low skive angle cutting permits transverse cutting of the strips.
U.S. Pat. Nos. 5,746,102 and 6,755,105 are examples of low angle cutters and methods of cutting cord reinforced assemblies including a carcass ply. The cutters have blades or wires that traverse across the width of the blade while cutting on a very low angle. The resultant cut ends are elongated and by being cut without heated blades exhibit no surface curing.
When cutting treads it has been found that it is often desirable to heat the knife blade to about 500 degrees F. (260 degrees C.) as is taught in U.S. Pat. No. 5,613,414 while cutting across a thick tire tread to increase cutting speed, but avoiding surface blooming of sulfur which tends to weaken the splice joint. In that patent it is disclosed that the prior art use of a guillotine cutter should be avoided wherein it is stated that prior art cutters for high mass, large cross-section components of rubber material have also included conduction-heated guillotine blades to plunge cut through the rubber material. There have been problems with this type of cutter because it utilizes a wedge-shaped blade which distorts the cut surface by compressing the trailing edge and elongating the leading edge. Splice control has been difficult which adversely affects tire uniformity. This prior art system is timer driven and the cut edges are exposed to the hot knife blade as it continues to plunge through the material. In addition the hot knife is positioned above the rubber material which has caused surface blooming. By surface blooming is meant surfacing of oils due to heat. Problems have also been experienced with incomplete cutting and rebound causing the leading and trailing cut edges to adhere after being cut. Control of the blade temperature has been difficult and slow because of the large thermally conductive mass. The time required for replacement of the blades has also been substantial because the larger mass involved requires considerable time for cooling.
While the use of guillotine type cutters has some noted drawbacks it is undisputed that the ability of a guillotine blade to cut the strip through its relatively thin cross sectional thickness as compared to passing a blade or wire cutter across the entire transverse width of a strip is accomplished with far greater speed. Accordingly the rapid time the guillotine cutter accomplishes the task of cutting an elastomeric strip to length is an ideal feature if the other noted shortcomings can be overcome.
This is particularly true when cutting a relatively new tire component recently being incorporated into both passenger and truck tires that provides a built in sealant for punctures. In US patent publication 2005/0113502 a pneumatic tire with a built in colored sealant layer is disclosed. In that publication it is noted various pneumatic tires have been proposed which contain a built in sealant layer based on a depolymerized butyl rubber layer, the list including those described in U.S. Pat. Nos. 4,895,610; 4,228,839; 4,171,237; 4,140,167 and patent applications U.S. Ser. No. 10/171,057 filed Jun. 13, 2002; Ser. No. 10/368,259 filed Feb. 17, 2003 and 11/126,503 filed May 11, 2005 among others.
For the most part these sealants include an organoperoxide component in their chemical composition that results in a depolymerization of a major portion of the uncured butyl rubber during vulcanization which exposed the material to heat which activates the process to create or form a very tacky material. Prior to exposure to heat the material is made into elongated strips as any other tire component. However, even though the material is made in strips of material the ability to cut such a layer to length and to form consistent splice ends has not been without difficulty. Any cutting technique that generates localized heating sufficient to start depolymerization at the surface needs to be avoided. Cold cutting tends to push the material much like trying to cut taffy, leaving non uniform ends for splicing and if successfully cut the ends will literally re-bond themselves together as though having never been cut due to the exceptional degree of tackiness of the material when cut.
Accordingly the inventors of the present invention have discovered a novel apparatus and method for cutting this type of material which greatly improves the uniformity and the time to cut such a strip of material to a desired length. Both the apparatus and the method are described hereinafter.